Infrared evidence for the formation of an intermediate compound during the synthesis of zeolite Na-A from metakaolin

Quantitative Infrared spectroscopy has been used to study the first step of the hydrothermal formation of zeolite Na-A from metakaolin. It is shown that metakaolin reacts with aqueous NaOH solutions, at room temperature, to give an amorphous solid, characterised by its IR spectrum. This compound, that has the same overall composition as zeolite Na-A must be regarded as the precursor of zeolite. At 60 degrees C, the IR spectra show that the precursor is first synthesised and that zeolite Na-A is formed only when metakaolin has been totally transformed. The formation of the precursor corresponds to the induction period observed by several authors when X-ray diffraction is used to follow the synthesis. (C) 1999 Elsevier Science Ltd. All rights reserved.